1. Field of the Invention
This invention relates to control valve devices in general, and more particularly to a control valve device which controls fluid communication in a fluid passage in response to both an input current signal from a switch device and changes in an engine ambient temperature.
2. Discussion of the Background
Valve devices of the type to which the present invention is directed are particularly well adapted for use in a carburetor outer vent control system of an automotive internal combustion engine and which prevents fuel evaporative gases produced in a carburetor float chamber from being discharged into the atmosphere. FIG. 1 shows a conventional example of the above carburetor outer vent control system wherein, when an engine ignition switch 11 is turned on to start the engine, an electric current is applied to a solenoid coil 13 from a battery 12 as an electric source. As a result, an electromagnetic valve 14 is maintained closed thereby blocking an fuel evaporative gas passage 15. This electromagnetic valve 14 is a normal open type valve which is maintained to be open when the switch 11 is at off-position. Therefore, the fuel evaporative gases produced in a carburetor float chamber 16 cannot be adsorbed on a canister 17 during engine operation. In this case, the fuel evaporative gases are supplied to the engine through an inner vent tube 18 and an air-fuel induction passage of a carburetor 21, and then are burned.
Next, when the engine is stopped, no electric current is applied to the solenoid coil 13 to thereby maintain the electromagnetic valve open. At this time, the ambient engine temperature is still high and fuel in the float chamber 16 is evaporated. The evaporated fuel gases are adsorbed on the canister 17 by means of the electromagnetic valve 14 positioned in the fuel evaporative gas passage 15 and by means of the thermal responsive control valve 20, thereby preventing the fuel evaporative gases from being discharged into the atmosphere. The control valve 20 is maintained open at a high temperature (over approximately 50.degree. C.), and closed at a low temperature, respectively.
As time proceeds after the engine is stopped, the engine temperature falls. When the temperature falls below a predetermined value, the control valve 20 is maintained closed to thereby prevent the fuel evaporative gases from being adsorbed on the canister 17. However, since the fuel only slightly evaporates owing to the drop of the fuel temperature within the float chamber 16, it is not a serious problem even if adsorption of the canister 17 is interrupted.
As shown in FIG. 1, the carburetor 21 is of the downdraft type having the air-fuel induction passage 19 at one end thereof and connected to an engine intake manifold 22 at the opposite end thereof. The induction passage 19 includes a throttle valve 23 which is rotatably mounted on a part of the carburetor body across the passage 19 in a manner to control the flow of air-fuel mixture into the intake manifold 22.
In the conventional carburetor outer vent control system shown in FIG. 1, however, both the electromagnetic valve 14 operable in response to the ignition switch 11 and the thermal responsive control valve 20 operable in response to changes in the engine temperature are separately constructed. Therefore, the number of parts constituting the control system 10 will increase and then the control system 10 becomes a larger size, whereby it may be difficult to install the control system 10 on the internal combustion engine. Furthermore, the thermal responsive control valve 20 operates in response to changes in an ambient temperature in the vicinity of the carburetor 21. Since this ambient temperature is not exactly the same as the temperature in the carburetor float chamber 16 with the result being that a certain difference in temperature may be observed, the outer vent control system 10 cannot operate with high accuracy in response to changes in the temperature of the float chamber 16.